1. Field of Invention
Embodiments of the invention generally relate to a method for tuning manifolds for an internal combustion engine.
2. Background of Prior Art
A multi-chamber, internal combustion engine includes intake ports for delivering fuel and air to combustion chambers where the air/fuel mixture is ignited. Combustion by-products are channeled out of the combustion chamber through exhaust ports into a manifold. The manifold serves to merge the combustion by-products from the individual combustion chambers together to form a single stream of combustion by-products. The combustion chamber is typically defined by a piston and cylinder, or a rotor and peripheral housing.
For example, a typical inline four-cylinder engine has an intake and an exhaust port for each cylinder. Each exhaust port is coupled to a manifold by an individual inlet, called a primary. Within the manifold, the four primaries merge into a single outlet port called a collector, which channels the combustion by-products away from the engine for subsequent exhausting to the atmosphere.
In typical engine designs, the distance between the individual primary inlets and the collector merge point is not a functionally critical specification; i.e., individual primary lengths are not selected with an intent to improve flow, thermal characteristics, scavenging, or other aspects. Conventionally, the standard criteria for establishing individual primary lengths are based upon convenient fitment or geometric constraints.
Primaries designed using convenience or bulk/average criteria are generally connected from primary inlet to collector merge point by the simplest, most convenient route with no other consideration to the performance consequences of individual primary lengths.
Primaries designed using an equal length criteria are constrained in that the distance between each primary inlet and collector merge point is precisely the same (equal) distance.
Another common primary design is multiple merge primaries, where more than one merge collector exists between primary inlet and final collector merge point. For example, in an inline four-cylinder engine having four exhaust inlet primaries, the inlet primaries are cascaded together in pairs via two-inlet, one-outlet collectors. In this example, the two pairs of exhaust inlet primaries first join in two independent merge collectors, each with two inlets and an independent outlet. Then, the two collector outlets are merged together into a third collector, also with two inlets and one final outlet. This design is sometimes referred to as xe2x80x9cTri-Yxe2x80x9d design because of the three y-shaped, two-inlet, one-outlet merge collectors.
In addition to these non-functional design criteria, some functional methodologies for designing exhaust systems have been used to improve engine performance. One example is U.S. Pat. No. 5,216,883 (Flugger), which describes a header assembly for internal combustion engines. Flugger discloses a header assembly designed to improve engine horsepower by using an expanding collector to lower the pressure in the exhaust header in order to improve scavenging, the process by which combustion by-products are removed from the combustion chamber. Flugger also discusses other methodologies which attempt to improve engine performance via exhaust header design. These design methodologies mainly focus on either the overall header design or the design of the collector itself.
Another example of an exhaust manifold designed using functional considerations is known as a stepped primary. In this design, the internal cross-sectional area of the primary increases or decreases along its length to the collector point to control the speed of a gas pulse traveling through the primary. The momentum energy from each gas pulse is used to improve the engine""s exhaust scavenging process. However, although the length of the primary is an attribute in the determination of the dwell time of the gas pulse within the primary, ultimately the timing of the gas pulse is controlled by varying the cross-sectional area with little or no consideration to the choosing of an exhaust primary length as a basis of improving performance. Moreover, the utilization of primaries having varied cross-sectional area disadvantageously increases the cost of the engine of the primary.
Therefore, there is a need for a method for selecting engine primaries to enhance engine performance.
A method for primary length tuning of intake and exhaust manifolds in internal combustion engines is provided. In one embodiment, the method calculates optimal exhaust primary lengths in order to utilize the momentum energy of each exhaust pulse and to maximize wave pulse scavenging of the exhaust.
In one embodiment, a method for tuning an intake/exhaust system of a multiple chamber, non-sequentially fired internal combustion engine having a plurality of combustion chambers and an at least equal number of primaries coupled to at least a first bank, wherein each of the primaries is independently coupled to a different one of the plurality of combustion chambers, the method including the steps of assigning a base length to one of the primaries that is connected to the chamber which has the shortest elapsed time in combustion events between the chamber and a subsequent firing chamber for each bank, and determining primary lengths for the remaining primaries in each bank, where a differential between the primary lengths is directly proportional to the elapsed time in combustion events between the chamber in the bank coupled to the primary and a subsequent firing chamber within the bank.